26 July 2006

The Prowling Naturalist: Bukit Timah II: Visiting the Reserve

At only 163 m., it was a fairly easy climb to the summit of Bukit Timah in the pre-dawn darkness last Monday, along the paved Main Road and then up a steep slippery shortcut abutting what is called, for unspecified reasons, the Police Repeater Hut. (This structure, surrounded by a wire mesh fence, has dire warnings posted against potential trespassers and, it being Singapore, you should take these seriously. To play it safe, I’ve always averted both my gaze and my camera whenever I’m in its vicinity.) Sunrise at Bukit Timah came over the city and, so close to the Equator (only 137 km. south of where we were), dawn was a short fleeting affair. You can’t really see the city from the summit itself but a VHF station on an adjoining lesser peak provides a good view, especially when the sun is coming up. Around dawn, the Main Road and the summit began to fill with scores of health seekers carrying out complicated exercises, many of which involved walking backwards and flailing and clapping their hands. (I will leave it to cultural anthropologists to study the amazing rituals now evolving in Singapore.) Birding, for which I was up so early, was expectedly terrible in the midst of all this commotion. It was far from the peaceful beginning of the day that I had anticipated, going by what it had been like ten years ago. Between 1996 and now Singaporeans seem to have really discovered their one remaining rain forest and turned it into an open air gym.

At present the Bukit Timah Nature Reserve is about 164 ha. but only 70 ha. of it is was never cleared even in Wallace’s day, presumably because much of this core lies along steep slopes that were logistically difficult to log. The area was first made into a Forest Reserve in 1886 when only 122 ha. remained forested [1]. Attempts at restoration by tree planting began in the late 1880s. By then, granite quarries on the south and west of the central hill (Bukit Timah proper) were already having an impact on the forest. In the 1930s, the northeast side was taken over by a dairy farm. By 1936 Singapore’s forest reserve system had been abolished and Bukit Timah was administered as an unofficially protected area by the Singapore Botanical Gardens. By 1950 the protected area had reached its minimum size and, in 1951, the Nature Reserve Act finally designated it as a Nature Reserve dedicated to nature conservation. Extensive reforestation began in the surrounding Catchment area some time in the 1980s. The forest has not been slow to recover showing what concerted restoration can do even in the middle of a city with a population over 3 million.

The core today is a typical Southeast Asian coastal hill dipterocarp forest [2] dominated by seraya (Shorea curtisii) but with at least eight other dipterocarp species. But even this primary forest is far from undisturbed. There’s ample evidence that an occasional tree has been removed here and there, presumably illegally. Granite mining has taken its toll throughout Bukit Timah (which is composed entirely of soils derived from granite). Worse, 11 February 1942 saw the Battle of Bukit Timah between the British and the Japanese for control of the strategic highest point of the island. Signs of the military operations remain even today. Several hiking trails cut through the core area, and the Reserve typically gets over a thousand visitors every day. There are many bicycle trails including an over-used one that circles the Reserve on low ground. Perhaps all this attention will help conservation somewhere some day but, right now, some rationing of visitors to Bukit Timah itself is probably in order.

Luckily almost all the visitors stick to the Main Road and a few of the less demanding hiking trails. At the summit, much of the crowd disappeared around 8 a.m. and birding finally became possible. The sound of Green-bodied Cicadas (Dundubia sp.) began to compete with that of the not-so-distant traffic from the highway below. (Overflying aircraft are a constant presence at Bukit Timah.) A Greater Racket-tailed Drongo (Dicrurus paradesius) tried ineffectively to capture a fluttering white butterfly. Somehow the insect managed to escape and the bird settled down disconsolately on an overhanging branch, its glistening upperparts turning blue-green in the emerging sun. The find of the morning was a dainty red and black Crimson Sunbird (Aethopyga siparaja) that flitted from tree to tree. There were Dark-necked Tailorbirds (Orthotomus atrogularis) and Olive-backed Sunbirds (Nectarinia jugularis). I identified over twenty species within the hour once the crowd had melted away.

There’s ample reason to believe that mammals are in decline within the Reserve though there are no hard data yet. In 1996 long-tailed macaques (Macaca fascicularis) were fairly common; this week I saw no trace of one even though the signs that remind you not to feed the monkeys are still there in abundance. The only common mammal was the plantain squirrel (also called the red-bellied squirrel, Callosciurus notatus). Perhaps strangely, though this augurs well for the future of the Reserve, alien mammals have so far not been able to establish their presence with it [1]. Epiphytes are also clearly in decline, going by my memory from ten years ago. Inside the rain forest, as usual, birds were heard more often than they were seen. My goal was to walk all the hiking trails, something I hadn’t managed in 1996, and it took me most of the day. The forest cover was an escape from the heat and humidity, as it also had been for Wallace. By and large, the more strenuous trails—the Jungle Fall path, the Seraya Loop (rich in Shorea curtisii, as you’d expect), the Tiup Tiup Path, and the Catchment Path—were all deserted.

We know much more about Bukit Timah—at least about the vegetation in the primary forest—now than we did in 1996 thanks to a rather remarkable ongoing monitoring project [1]. In 1993, the Center for Tropical Forest Science (CTFS) of the Smithsonian Tropical Research Institute in collaboration with the Arnold Arboretum (AA) of Harvard established a 2-ha. permanent study plot in Bukit Timah to monitor changes in the vegetation. This project is loosely coupled to a suite of 50-ha. tropical plots established worldwide for the same purpose with the encouragement of CTFS. In Asia these include Mudumalai in South India (where my friend Raman Sukumar works), Sinharaja in Sri Lanka, Huai Kha Khaeng and Khao Chong in Thailand, Pasoh in peninsular Malaysia, Lambir in Sarawak, and Palanan in the Philippines. The plot in Bukit Timah is a little different. For one thing, it is much smaller than the others. For another, the purpose here has been to understand what happens in a fragment subject to continuous and varied human disturbance, rather than in a remote undisturbed forest.

While the plot in Bukit Timah is in primary forest, it is not undisturbed, with the Tiup Tiup Path running right through it. Luckily this does not appear to be among the most popular trails. The plot has been censused in 1993, 1995, 1997, and 2003 for all trees with a diameter at breast height (dbh, roughly 1.3 m.) greater than 1 cm. We can now see what trends, if any, have emerged during a decade. In 1993 there were 12 952 trees which had decreased to 11 467 in 2003. The number of trees per hectare is comparable with similar forests elsewhere in the world though lower than that at some places such as the Lambir Hills in Sarawak. However, while there were 326 tree species in the Bukit Timah plot 1993, there were 328 in 2003. (These numbers are greater than the number of tree species in the entire United Kingdom, driving home how biologically rich tropical regions are.) The only group that is obviously in trouble are species of nutmeg which is not bad for such a tiny isolated forest. However, indices of evenness, for instance, measured by Shannon’s index, give Bukit Timah lower scores than almost all other similar areas in the neotropics and in Asia, though not in west Africa [1]. There has not been significant changes in these indices during the last decade.

The small decline in the total number of trees may also be due to the fact that the original plot was explicitly chosen because it contained a large grove of mature trees [1]. That some of them died without being replaced by recruits may be no great source of concern. But this raises a troubling question of research design: the plot was is in no sense selected to be representative of the forest as a whole. Do results from it say anything about the general trends at Bukit Timah? Perhaps not. The CTFS-AA collaboration should take questions of its research design more seriously, a point that is equally applicable to most of the 50-ha. tropical sites that are being monitored worldwide as it is here. Otherwise there is less genuine scientific payoff than possible, given all the money and effort expended on these projects.

Should you organize a trip to Bukit Timah to see a rain forest for the first time? Almost certainly not—save that for Endau-Rompin further up the peninsula in Malaysia. Or even the over-used Taman Negara which has increasingly become more of a resort than a national park. But, if you just happen to be in Singapore, as I was this week, few sights are as interesting as this rain forest in the middle of an industrialized city. If I return to Singapore, I know that I’ll be back at Bukit Timah even though there are several other new reserves in Singapore that I haven’t seen, in particular, the Sungei Buloh Nature Park consisting of an 87-ha. wetland important for migratory birds.